The objective of this study is to provide some fundamental data regarding degenerative and possible regenerative changes in the mammalian central nervous system. The first part of the study is concerned with a quantitative study of retrograde neuronal changes in Clarke's column relating the degree of neuronal death and chromatolysis to the age of the animal, the post-operative survival period, and the proximity of the axonal lesion to the cell perikarya. Data will be obtained from neuron counts and cell measurements of material stained by the Nissl method. The second part involves a study of axonal sprouting of dorsal roots in the spinal cord and medulla after chronic primary deafferentation and utilizes the Nauta-Gygax and Fink-Heimer silver methods in conjunction with the autoradiographic method for tracing neuroanatomical connections. This part of the investigation is being undertaken because of controversy regarding the contradictory evidence for sprouting as seen in light microscopic studies in the adult animals. The third part involves a study of the descending connections from the brainstem to the spinal cord, with particular emphasis on central autonomic pathways using the anterograde and axonal transport of various marker materials as well as immunohistochemical techniques. The fourth part involves a study of autonomic pathways in the spontaneously hypertensive rat and the potential effects of 6-hydroxydopamine on these pathways that might be related to blood pressure control.